Verificationism

Verificationism, also known as the verification principle or the verifiability criterion of meaning, is the philosophical doctrine that only statements that are empirically verifiable (ie. verifiable through the senses) are cognitively meaningful.

The verifiability criterion underwent various revisions throughout the 1920s to 1950s, but, by the 1960s, was deemed to be irreparably untenable. Its abandonment signaled the end of the entire movement launched by logical positivism.[2]

Logical positivists within the Vienna Circle quickly recognized that the verifiability criterion was too stringent. Notably, all universal generalizations are empirically unverifiable, such that, under verificationism, vast domains of science and reason, such as scientific hypothesis, would be rendered meaningless.[7]

In 1936, Carnap sought a switch from verification to confirmation.[7] This confirmability criterion would not require conclusive verification (thus accommodating for universal generalizations) but allow for partial testability to establish "degrees of confirmation" on a probabilistic basis. Carnap never succeeded in formalizing his thesis despite employing abundant logical and mathematical tools for this purpose. In all of Carnap's formulations, a universal law's degree of confirmation is zero.[11]

That same year saw the publication of A J Ayer's work, Language, Truth and Logic, in which he proposed two types of verification: strong and weak. This system espoused conclusive verification, yet accommodated for probabilistic inclusion where verifiability is inconclusive. Ayer also distinguished between practical and theoretical verifiability. Under the latter, propositions that cannot be verified in practice would still be meaningful if they can be verified in principle.

Karl Popper's The Logic of Scientific Discovery proposed falsificationism as a criterion under which scientific hypothesis would be tenable. Falsificationism would allow hypotheses expressed as universal generalizations, such as "all swans are white", to be provisionally true until falsified by evidence, in contrast to verificationism under which they would be disqualified immediately as meaningless.

Though widely recognized as a revision of verificationism,[5][12] Popper intended falsificationism as a methodological standard specific to the sciences rather than as a theory of meaning.[5] Popper regarded scientific hypotheses to be unverifiable, as well as not "confirmable" under Carnap's thesis.[5][13] He also found unscientific, metaphysical, ethical, and aesthetic statements often rich in meaning and important in the origination of scientific theories.[5][14]

Although Karl Popper's falsificationism is widely criticized by philosophers, Popper has been the only philosopher of science often praised by scientists,[13] whereas verificationists have been likened to economists of the 19th century who took circuitous, protracted measures to refuse falsification, that is, refutation, of their preconceived principles.[19] Still, logical positivists practiced Popper's principles—conjecturing and refuting—until they ran their course, catapulting Popper, initially a contentious misfit, to carry the richest philosophy out of interwar Vienna.[12] And his falsificationism, as did verificationism, poses a criterion, falsifiability, to ensure that empiricism anchors scientific theory.[3]

In a 1979 interview, A J Ayer, who had introduced logical positivism to the Anglosphere in the 1930s, was asked what he saw as its main defects, and answered that "nearly all of it was false".[18] Still, he soon admitted still holding "the same general approach".[18] The "general approach" of empiricism and reductionism—whereby mental phenomena resolve to the material or physical, and philosophical questions largely resolve to ones of language and meaning—has run through Western philosophy since the 17th century and lived beyond logical positivism's fall.[18]

In 1977, Ayer had noted, "The verification principle is seldom mentioned and when it is mentioned it is usually scorned; it continues, however, to be put to work. The attitude of many philosophers reminds me of the relationship between Pip and Magwitch in Dickens's Great Expectations. They have lived on the money, but are ashamed to acknowledge its source".[3] In the late 20th and early 21st centuries, the general concept of verification criteria—in forms that differed from those of the logical positivists—was defended by Bas van Fraassen, Michael Dummett, Crispin Wright, Christopher Peacocke, David Wiggins, Richard Rorty, and others.[3]

^ abJames Fetzer, "Carl Hempel", in Edward N Zalta, ed, The Stanford Encyclopedia of Philosophy (Spring 2013): "However surprising it may initially seem, contemporary developments in the philosophy of science can only be properly appreciated in relation to the historical background of logical positivism. Hempel himself attained a certain degree of prominence as a critic of this movement. Language, Truth and Logic (1936; 2nd edition, 1946), authored by A J Ayer, offers a lucid exposition of the movement, which was—with certain variations—based upon the analytic/synthetic distinction, the observational/theoretical distinction, and the verifiability criterion of meaningfulness.

Hempel (1950, 1951), meanwhile, demonstrated that the verifiability criterion could not be sustained. Since it restricts empirical knowledge to observation sentences and their deductive consequences, scientific theories are reduced to logical constructions from observables. In a series of studies about cognitive significance and empirical testability, he demonstrated that the verifiability criterion implies that existential generalizations are meaningful, but that universal generalizations are not, even though they include general laws, the principal objects of scientific discovery. Hypotheses about relative frequencies in finite sequences are meaningful, but hypotheses concerning limits in infinite sequences are not. The verifiability criterion thus imposed a standard that was too strong to accommodate the characteristic claims of science and was not justifiable".

^Despite Hume's radical empiricism, set forth near 1740, Hume was also committed to common sense, and apparently did not take his own skepticism, such as the problem of induction, as drastically as others later did [Antony G Flew, A Dictionary of Philosophy, rev 2nd edn (New York: St Martin's Press, 1984), "Hume", p 156].

^"But for a brief lapse around 1929/30, then, the post-AufbauCarnap fully represents the position of Vienna Circle anti-foundationalism. In this he joined Neurath whose long-standing anti-foundationalism is evident from his famous simile likening scientists to sailors who have to repair their boat without ever being able to pull into dry dock (1932b). Their positions contrasted at least prima facie with that of Schlick (1934) who explicitly defended the idea of foundations in the Circle's protocol-sentence debate. Even Schlick conceded, however, that all scientific statements were fallible ones, so his position on foundationalism was by no means the traditional one. The point of his 'foundations' remained less than wholly clear and different interpretation of it have been put forward. ... While all in the Circle thus recognized as futile the attempt to restore certainty to scientific knowledge claims, not all members embraced positions that rejected foundationalism tout court. Clearly, however, attributing foundationalist ambitions to the Circle as a whole constitutes a total misunderstanding of its internal dynamics and historical development, if it does not bespeak wilfull ignorance. At most, a foundationalist faction around Schlick can be distinguished from the so-called left wing whose members pioneered anti-foundationalism with regard to both the empirical and formal sciences" [Thomas Uebel, "Vienna Circle", sec "3.3 Reductionism and foundationalism: Two criticisms partly rebutted", in Edward N Zalta, ed, The Stanford Encyclopedia of Philosophy (Summer 2012 edn)].